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August 12, 2012

Gravel Bike Build - Part 2

Or go back to Gravel Bike Build - Part 1
So many of the decisions to make on the bike are dependant on each other. For instance, the 1x10 drivetrain that I want. I have a SRAM 10 speed chain that I won at the ICC 12hr earlier this yeah. Chains ain't cheap, so I'd like to use this free one. I also already have a Truvativ Elita 2x10 crankset with 39-53 chainrings that was a take-off from an old Giant road bike. And I still have the SRAM bottom bracket from the old Giant. It may not be a good call re-using a bearing set, but I'm going to go with it for now and call it my proof-of-concept phase. This whole 1x10 idea may blow up in my face. I haven't found anyone that made it work with this same frame. Plus if it makes problems later it's not a big deal to change.

I want to go with the single front chain ring for simplicity. Fewer parts to break and wear, less maintenance, and fewer things to think about when riding. Also will benefit from a slight weight reduction from the 'missing' parts - chainring, cables, derailer, shifter. That sounds a lot like a singlespeed rider talking, but I'm not a strong enough rider for that yet. So I'll be putting a 11-34 mtn bike cassette in the rear for a good spread of shifting options.

The first part going on the bike is the bottom bracket. You should measure this yourself before buying parts, but a good source to check the size is Bikepedia. Here's the link to my frame.

This frame has a 68mm width and English threads. English threads are 1.37 inch dia x 24 tpi (threads per inch).

Bikepedia says this frame originally came with an integrated ISIS style bottom bracket, but I'm going to updated it with an external bearing set. The new style external bearing sets have great seals and are easy to replace. With the dirt and gravel dust I expect this bike to see, good seals are a must. I am using a SRAM GXP.

If you want a single place to geek out on the bewildering assortment of bottom brackets available and some of the pluses and minuses of all the different types, here is a good link. Like anything else cycling-related you can spend crazy money here on carbon fiber shells and ceramic bearing.

One new thing I learned is that SRAM BB's and Shimano BB's are not interchangeable. Shimano BB's and cranksets have the same spindle diameter for both drive and non-drive side bearings. SRAM uses a larger diameter drive side bearing. You have to use SRAM BB's with SRAM/Truvativ cranksets.

Now that I have the right BB, it was time to install it:

Put a small dab of grease on the threads (don't blow this off - you may never get it out again when it needs replacing):

To install the BB you will need a specific tool. The only one to get is the socket type. You have to torque bottom brackets - the handheld wrench type tool will not let you get a proper torque measurement. And for God's sake don't try this with pliers or a pipe wrench. The grooves in the BB are soft aluminum and will shred without the right tool. Here is the one I use: Park Tool.

This BB gets torqued 25-30 ft lbs, it is printed right on the cup so you can't make a mistake. Don't cheat on this and take your best guess. The BB threads are steel, the frame is aluminum. You can over-torque and ruin the frame threads, or under-torque and listen to a creaky noisy BB with every pedal stroke. I have the 'click-type' wrench for ft lb ranges. So set up the torque wrench to 28 ft lbs and go:

Repeat for the drive-side. Watch out for the drive-side though, it has left hand threads so you will be threading and torquing in the opposite direction. (the old lefty-loosey, righty-tighty don't work here)

10 comments:

I don't know for sure about 1x10, but I have 1x9 on my gravel bike and love it. The simplicity is nice, one less thing to mess up. Are you going to go with the 39 up front? I have a 42 on mine and a road cassette on the the rear and it is a little steep at times.

Chuck, I've got a couple of those Jandd framebags and they're great. I rode with one at DK and my only complaint is that they're a bit of a pain to open/close. I think it could be remedied with better zipper-pulls, though. I've got an extra you can borrow if I can find it.

Hi. I am sorry to contact you out of the blue, but I have a very specific question that it looks like you will have the answer to regarding 10 speed cassettes.

Here is my situation. I bought an old MTB frame that I would like to build up as a 1X10 gravel/fire road bike with brifters. I am very confused with all of the Dynasys equipment and whatnot.

Can I use a Dynasys cassette with a 9 speed MTB derailleur? If so, will I get all 10 speeds? I would like to run an 11-34 cassette with a 39T chain ring. My plan at this point is to use Campy shifters and some sort of cantis, but everything is very preliminary at this point.

You really seem to have a great handle on this stuff. Thanks in advance for any help you can give a newbie doing his first bike build!